The present invention relates to additives for producing ductile and pure copper deposits from electrowinning, electrorefining and electroforming baths. More specifically, the present invention relates to polyepichlorohydrin trimethylamine quarternary additives useful in the electrowinning, electrorefining and electroforming of copper.
Electrowinning and electrorefining are methods of purifying and collecting copper for use in wire circuit boards or the like. In electrowinning, copper is plated directly from solution, using insoluble anodes such as lead. In electrorefining, the copper is plated onto a cathode from a soluble copper anode. These processes are known to those skilled in the art and have been in use since the 1800's.
In electrowinning applications, it has long been desirable to provide electrodeposits which do not require further purification. This has been problematic in two respects. First of all, additives commonly in use tend to oxidize on the insoluble lead anodes when they evolve oxygen. This anode phenomenon also leads to lead oxides which flake off during electrolysis. These unwanted particles will then tend to migrate to the cathodes, causing impurities of lead in the copper deposit. These impurities lead to low ductility in these deposits.
Guar gum has typically been used as a brightening additive for electrowinning. The drawback in using this additive is that it is hard to dissolve into solution and tends to readily break down. This creates erratic electroplating results. In electrorefining, thiourea is often used as an additive. This can result in sulfur co-deposition from the plating residues in the solution. Sulfur then co-deposits as an undesirable impurity in the copper deposit. Therefore, an additive without these disadvantages is desirable.
However, any additive used in electrowinning must also be compatible with solvent extraction of copper from the raw ore and the copper stripping process used in line for replenishing copper to the electrowinning baths. Typically, in order to extract copper from a raw ore, the copper ore is initially dissolved with a sulfuric acid solution. This also leaches many undesirable impurities from the ore. The copper is selectively extracted from the sulfuric acid solution via a solvent-solvent extraction technique. Such techniques are known. In brief, an organic solvent which is not soluble in the aqueous sulfuric acid solution is used. The organic solvent acts to exchange a hydrogen atom to the aqueous solution for a copper atom from the aqueous solution. After this is completed, the organic solvent having the copper ions attached is separated from the aqueous solution, leaving the impurities in the aqueous solution. After separation, the copper must then be stripped from the organic molecule.
Additives, to be useful, must not interfere or hinder this solvent extraction process. Hindrance of solvent extraction can occur in many ways. If an additive is too surface active, it will interfere with the organic water separation, leading to problems. Many organic molecules may interfere with the kinetics of the exchange reaction, reducing the efficiency thereof. Additionally, copper selectivity over iron is somewhat sensitive in the extraction system. Organic additives must not interfere with the selectivity of copper. Additives also must not interfere with the copper stripping process.
Improvements in purity of electrowinned and electroformed copper have been realized, such as by the use of novel polyacrylic acid additives, which are the subject of commonly assigned U.S. Pat. No. 5,733,429, issued Mar. 31, 1998, entitled "Polyacrylic Acid Additives for Copper Electrorefining and Electrowinning".
Ductility has increasingly become important in copper production. With the advent of micro-electronics, wired connections have gotten smaller and smaller. This means that the circuit conductors in microchips have become thinner and thinner. The limits, or the "fineness", of these conductors is directly proportional to the ductility of the copper used. The more the ductility of the copper, the more malleable it is. This allows the copper to be drawn or formed into thinner strands without breaking. As ductility decreases, copper becomes more brittle, hindering fine formation of thin circuit leads. Thus, high ductility copper is very much in demand.
Typically, in order to provide the purity and ductility necessary for such applications, it has been necessary for the electrowinned "rough" copper to be refined further, using various time consuming and expensive processes. Improvement in existing electrowinning and electrorefining baths is, therefore, desirable. Additionally, improvements in the ductility of electroformed copper is desirable, such that thinner gauge wire can be drawn from more ductile copper.